Example Questions

Example Question #1 : Understanding Meiosis

A scientist is interested in studying the event of crossing over (recombination) in mouse gametes. She wants to label some of the mouse DNA with fluorescent dyes to better visualize it. During what phase of the cell cycle should she look at these fluorescent DNA strands in order to most effectively study recombination?

Possible Answers:

Metaphase II

Anaphase II

Prophase I

Telophase I

Anaphase I

Correct answer:

Prophase I

Explanation:

Recombination or crossing over happens primarily in Prophase I. In anaphase and telophase, the DNA strands are separated and cannot recombine. In metaphase, homologous chromosomes line up with each other, but do not recombine.

Example Question #1 : Understanding Meiosis

Meiosis results in a halving of chromosomes in the daughter cells, while mitosis reserves the same amount of genetic material in the daughter cells.

Both use the same order of events: prophase, metaphase, anaphase, and telophase.

Both processes require DNA synthesis beforehand.

Both of these processes allow genetic variation.

Correct answer:

Both of these processes allow genetic variation.

Explanation:

Mitosis and meiosis share many procedural similarities, however, it is important to remember that mitosis makes identical cells while meiosis allows genetic variability between cells.

Meiosis takes place in sex cells, which are capable of creating millions of different variations of offspring. Mitosis takes place in normal cells involved in growth and regeneration within a single, uniform organism.

Example Question #1 : Understanding Meiosis

Which of the following highlights a key difference between meiosis and mitosis?

Possible Answers:

All answer choices are correct

There is no metaphase stage in meiosis

Genetic mutations can only occur in meiosis; mitosis always results in identical daughter and parent cells

Meiosis involves two divisions, while mitosis involves only one

Correct answer:

Meiosis involves two divisions, while mitosis involves only one

Explanation:

Meiosis includes two divisions, resulting in two pairs of haploid cells, while mitosis only involves a single division.

Both meiotic and mitotic divisions share the same phases, though there are some differences in the activity of these phases. Mutation can, and does, occur in both mitosis and meiosis. Crossing over, however, is unique to meiosis.

Example Question #4 : Understanding Meiosis

Crossing over during prophase occurs during which cycle of division?

Possible Answers:

All answer choices are correct

Meiosis I

Meiosis II

Mitosis

Correct answer:

Meiosis I

Explanation:

Crossing over ensures genetic variability as it results in daughter cells with different genetic material than their parent cells. This occurs during meiosis I, but is not seen in mitosis or meiosis II.

Example Question #1 : Understanding Meiosis

Which of the following chromosomal abnormalities is an example of monosomy?

Possible Answers:

Turner syndrome

Edwards syndrome

Down syndrome

Klinefelter syndrome

Correct answer:

Turner syndrome

Explanation:

Turner syndrome occurs when a person is missing one sex chromosome, and only has one X-chromosome. As a result, they will be female, and may suffer a variety of symptoms. This is an example of monosomy, in which a person only has one chromosome, when they should have two.

The other three choices are examples of trisomy. Klinefelter is an instance of sex-linked trisomy, with a karyotype of XXY. Down syndrome is cause by trisomy 21, and Edwards syndrome is caused by trisomy 18.

Non-disjunction occurs when sister chromatids fail to separate during meiosis, leading subsequent daughter cells to have an unequal number of chromosomes. This can result in a cell having one extra chromosome (trisomy), or missing one chromosome (monosomy).

The following shows non-disjuction occuring in metaphase II of meiosis. "X" represents a chromosome, "|" represents a cell membrane, and "\" and "/" represent chromatids. When a sperm cell fuses with the egg formed to the left of the membrane (|), it will result in trisomy. When a sperm fuses with the egg to the right of the membrane (|), it will result in monosomy.

Example Question #1 : Understanding Meiosis

Which of the following would result in a cell with an abnormal number of chromosomes after meiosis?

Possible Answers:

Nondisjunction

Cleavage of the securin protein

Recombination

Separation of sister chromatids

Correct answer:

Nondisjunction

Explanation:

Crossing over, or recombination, is a process that takes place in the earlier stages of meiosis and promotes genetic diversity. During recombination, genetic material is exchanged between two homologous chromosomes. The chromosomes ultimately contain the same amount of genetic material after recombination, and are properly separated during subsequent divisions.

The cleavage of the protein securin is actually what allows the sister chromatids to separate, a process that is essential to maintaining the correct number of chromosomes in each daughter cell.

Nondisjunction is the name given to the phenomenon in which separation of genetic material fails to occur. Either homologous chromosomes fail to separate properly in meiosis I, or sister chromatids fail to separate properly during meiosis II. The result of these nondisjunction events is one cell with an abnormally high number of chromosomes (for example trisomy) and one cell with an abnormally low number of chromosomes (for example monosomy).

Example Question #1 : Understanding Meiosis

Crossing over is an event that contributes to the non-identical nature of gametes. Which of the following is true regarding crossing over?

I. It occurs during prophase I

II. It involves exchange of genetic material between sister chromatids

III. It involves exchange of genetic material between homologous chromosomes

Possible Answers:

I

I and III

II

I and II

Correct answer:

I and III

Explanation:

Crossing over occurs during prophase of meiosis I (prophase I). This process requires tetrad formation, where the homologous chromosomes (with their sister chromatids) pair with each other. Following tetrad formation, the genetic material from one homologous chromosome can be exchanged with that of the other. This exchange of genetic material leads to genetic recombination and results in production of non-identical gametes. Crossing over occurs only between homologous chromosomes. Sister chromatids are situated to form a single chromosome; crossing over does not include recombination of genetic material within a single chromosome.

Remember that crossing over is not a mutation and is a completely natural process for every sexually reproducing organism.

Example Question #1 : Understanding Meiosis

Independent assortment of traits on different chromosomes is due to the random alignment of different pairs of homologues. This alignment occurs during which of the given phases?

Possible Answers:

Metaphase I

Prophase II

Prophase I

Metaphase II

Correct answer:

Metaphase I

Explanation:

Remember that the law of independent assortment states that genes on different chromosomes are passed independently of one another to offspring. This phenomenon results from the random alignment of the chromosomes along the metaphase plate. This random alignment allows genes to be segregated independently, and occurs during metaphase I.

Metaphase II involves the alignment of single chromosomes along the metaphase plate for segregation of identical sister chromatids. Remember that independent assortment is only valid for genes on different chromosomes. Genes on the same chromosomes are not passed independently of one another from parent to offspring.

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